For the tropical salsa: Meanwhile, combine the pineapple, avocado, cactus, jalapenos and mangoes in a medium bowl. Add the cilantro, vinegar, oil and epazote and toss to combine. Keep refrigerated until ready to serve.
For assembly: Preheat a grill to medium-high heat. Remove the shrimp from the marinade and sprinkle with salt. Place the shrimp on the grill over direct heat and cook, turning once, until they are charred and the flesh is pink, 2 to 3 minutes per side. Add the cooked shrimp to the salsa and toss to combine. Sprinkle with salt.
To serve, whisk together the crema, adobo, lime zest and lime juice in a small bowl. Build the tacos starting with a corn tortilla, add 4 to 5 shrimp, 1/4 cup tropical salsa, a drizzle of the crema mixture and some cilantro leaves.